A. Field of Invention
This invention relates to the preparations for topical application to human skin and, more particularly, to new and improved skin cream or lotion compositions, which are especially useful in affecting the aging process of human skin.
B. Description of Related Art
The aging process of skin has been characterized by two main factors, the loss of elasticity and the loss of moisture, both of which are continuously lost over the course of the average human lifetime. Commercially available topical preparations have been designed to increase the moisture content of the skin. Most of the available topical moisturizing products provide only a short-term replenishment of moisture-providing ingredients. Some of such products contain glycolic acid alone and with other acids such as citric acid. Collectively, these acids may be referred to as "fruit acids," or "alpha-hydroxy" acids. The fruit acids are known to be capable, when applied to the skin, of aiding in the removal of older, dead, or keratinized skin cells, a process referred to as exfoliation. Exfoliation results in the exposure of the softer, younger skin cells, which otherwise lay below the older cells, and in this manner, exfoliation results in softer, younger appearing skin. Another positive consequence of the removal of the dead skin cells is that the still living, younger skin cells which are now exposed, produce, as a protective mechanism, increased amounts of at least one type of glycosaminoglycan molecule. Glycosaminoglycan molecules produced by the skin include hyaluronic acid, chondroitin sulfate, and dermatan sulfate. Hyaluronic acid is known to be produced in higher quantities by the skin cells in response to exfoliation. Hyaluronic acid has a large capacity for hydration. One gram of hyaluronic acid is able to hydrate to a volume of 3 liters. The exposed, younger skin cells produce more hyaluronic acid than the older cells provided there are present sufficient substrates and co-factors required for hyaluronic acid synthesis by the skin cells. As a result, after exfoliation with fruit acids, a higher concentration of hyaluronic acid is produced in the skin. The hyaluronic acid, being a hydrating molecule, and being located deeper in the skin than topically applied hyaluronic acid or other topically applied moisturizers results in the ability of fruit acid application to the skin to act as, in effect, a long term moisturizer. The length of time of increased hydration of the skin can vary depending on the concentration and number of applications of fruit acids, as well as the endogenous stores of substrates and co-factors that are required and available to the skin for hyaluronic acid production. The combination of the two effects of topically applied fruit acids, exfoliation and increased skin production of hyaluronic acid, is believed to result in a lessening of the appearance of skin wrinkles.
A negative consequence of the reliance upon exfoliation to appreciatively increase the amount of hyaluronic acid in the skin is that the skin, having been stripped of its protective layer of keratinized cells, is relatively unprotected but nevertheless is exposed to the elements. The younger, unprotected skin is susceptible to damage by environmental factors such as chemicals, and sunlight. It is also noted that after long-term use of fruit acids for exfoliation, endogenous stores of substrates and co-factors required for the production of hyaluronic acid can become depleted. As a result, the hyaluronic acid content, and subsequently the moisture content of the skin can actually be reduced by long-term, or chronic topical use of fruit acids in concentrations capable of exfoliation. Another disadvantage of the use of fruit acids is the fact that their use has been associated with a significant amount of irritation.
Many skin cream compositions which are commercially available also address the other major component of skin aging, the loss of elasticity, through the use of moisturizers. One of the mechanisms of the loss of elasticity in aging skin is through the loss of elastin, a human protein which is a major component in elastic fibers and provides the skin with much of its elastic qualities. The break down of elastin is characterized by the deposition of lipids in the protein fold, followed by the attraction, by the lipids, of mineral salts. The accumulation of mineral salts, in particular calcium, decreases the elasticity of the elastin, and when the elastin molecule loses enough of its elasticity and becomes rigid, the molecule will break rather than elongate if enough tension is applied. When the elastin molecules break down, they are removed by endogenous immune surveillance mechanisms and may not be replaced at the same rate, resulting in a net loss of elastin in the skin tissue. At the area at the lateral folds of the eyes, the forehead, and on the neck, the chronic net loss of elastin, allows for the formation of wrinkles. Some commercial products include the molecule elastin in their formulations, However, as is the case with skin care moisturizers, there is no evidence that this exogenous elastin penetrates to a level that would be helpful, or that it remains in the skin long enough to provide any level of protection from, or reversal of, wrinkles. The known, available skin care products have not been demonstrated to interfere with the break down of elastin and the age-associated decrease in skin elasticity which in part characterizes the aging process of skin.